no worries about parts and appendices

Added fixes and work arounds for books with parts and/or appendix. Earlier version would crash.
Added optional yaml key chapno to specify the chapter letter as prefix for custom numbered blocks in html books, and attribute secno to level 1 headings for pdf books.

v0.1.1: fixes

fixes:

• example was not working due to a shortcut in an html comment
• a recent fix to make references work in quarto book had broken the filter for ordinary documents

v0.1.0: box, number and ship my theorems and friends

Initial release of a (mostly) working quarto extension that numbers, styles and cross references user defined blocks (html divs / latex environments).

There is an issue with list-of-blocks when rendering books which will be fixed in the next release.